Background. COPD is a common chronic health condition. Because current medical treatments have minimal impact on disease progression, a strategy to prevent COPD-related disability would have important clinical and public health benefits. Study Aims. To elucidate the disablement process, we will test a specific conceptual model of how disability develops in COPD. The aims are: (1) To evaluate the impact of respiratory impairment, especially pulmonary function impairment, on the risk of functional limitation in COPD. Using a control group, to elucidate the prevalence of respiratory impairment, functional limitation, and disability that is directly attributable to COPD. (2) In adults with COPD, to delineate the longitudinal effect of functional limitation on the risk of incident disability. We hypothesize that development of functional limitation, and not pulmonary function impairment, is the major determinant of disability. (3) To determine the prospective impact of disability on the risk of future adverse health outcomes. Methods. We will assemble a prospective cohort of 1200 randomly sampled adults with COPD who are members of a large regional health maintenance organization. A matched control group of 300 subjects will be recruited. Subjects will undergo a detailed physical assessment that measures respiratory impairment (e.g., pulmonary function) and functional limitation (e.g., lower extremity function, muscle strength, exercise performance, and cognitive function). Structured telephone interviews will ascertain disability outcomes at baseline and 18-month prospective follow-up. We will also study the modulating effects of specific risk factors and protective factors on the progression from functional limitation to COPD-related disability, including psychological factors, environmental exposures, and health care process factors. Significance. Elucidation of the disablement process is the first step toward designing clinical and public health interventions that target reduction of disability in COPD. By determining the pathway from functional limitation to disability, our goal is to provide a scientific basis for screening and prevention of disability among persons with COPD. Based on this work, intervention strategies can be designed that target reduction of functional limitation and disability to improve downstream health outcomes.